I had one weirdo ECG question, where they gave me just the strip and then asked me the diagnosis. I don't want to divulge the question, but it was an electrolyte issue they were asking about that WASN'T K or Ca related. No background info on the patient except that they were elderly, in a nursing home. Still not entirely sure what the answer was- there were ~10 options for an answer, so I ruled out hyper or hypo K and Ca and then just picked one, since I knew what those would look like and it definitely wasn't that.
Basically, it's possible you'll get something off the wall. But you CAN'T study for everything, and it's waaaaay more likely you'll get a simple one out of FA.